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Патент USA US3086190

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April 16, 1963
3,086,180
J. ARNAUD ETAL
DELAY LINE FOR TRAVELLING WAVE TUBES
Filed Feb. 17, 1959
2 Sheets-Sheet 1
aLoti,n;‘
INVENTORS
J.ARNAUD
By
& 19- 11:27:51
K ‘ <11 ?fe“
ATTORN EY
April 16, 1963
3,086,180
J. ARNAUD ETAL
DELAY LINE FOR TRAVELLING WAVE TUBES
Filed Feb. 17, 1959
2 Sheets-Sheet 2
16'
F1:9. 10
F19.”
INVENTORS
J. AR/YAUD
t? .B- PSZTf/N
BY
K‘ 9‘ ff
7
ATTORNE
States
" satent‘
1
3,086,180
Jacques Arnaud, Paris, France, and Bernard Epsztein,
DELAY LINE FOR TRAVELLING WAVE TUBES
Jamaica, N.Y., assignors to Compagnie Generale de
Telegraphie sans Fil, Paris, France
Filed Feb. 17, 1959, Ser. No. 793,835
Claims priority, application France Feb. 27, 1958
21 Claims. (Cl. 333-31)
3,086,180
,.
IQQ
‘Patented Apr; 16, 1963
2
wave tube ampli?ers in which the danger of deformation
of the individual delay line elements is minimized by per
mitting the same to freely expand under the in?uence of
heat generated by the power dissipated in the tube.’
A still further object of the present invention is to pro
vide a delay line circuit for travelling wave tube ampli
?ers adapted to operate at relatively elevated power rat
ings which prevents the ampli?cation of undesired modes
at the wave lengths for which the tube is intended to op
The present invention relates to a‘ delay line for elec 10 erate as ampli?er with a predetermined mode.
These and other objects, features and advantages of
tron discharge devices and, more particularly, to a rugged
the present invention will become more apparent from
delay line structure for use in high~power travelling wave
the following description when taken in connection with
tubes.
At present in high-p ower travelling wave ampli?er tubes,
the accompanying drawing, which shows, for purposes
a delay line circuit is used which is constituted by a 15 of illustration only, several embodiments in accordance
with the present invention and wherein:
ladder-type line, disposed essentially parallel to a metallic‘
FIGURE 1 ‘is a partial perspective view of a delay line
surface usually designated as “back plate” which en
circuit of the prior art;
ables the attainment of a relatively smaller dispersion.
FIGURES 2 and 3 are diagrammatic showings of the
Such prior art structure as used in travelling wave
tubes is represented, for example, in FIGURE 3 of the 20 ?eld distribution on the bars or delay elements of the
ladder-type delay lines;
French Patent 1,068,673 of June 28, 1952 taken out in
FIGURE 4 is a partial perspective view of a delay line
the name of the assignee of the present application.
circuit in accordance with the present invention;
In practice, in order ‘to avoid thermal deformations of
FIGURES 5 and 6 are diagrammatic showings of the
the individual elements or bars of the ladder~type struc
ture, it is necessary to split or separate the same in the 25 ?eld distribution on the T-shaped delay elements of the
delay circuit of FIGURE 4;
center thereof to provide a gap or slot thereat in such
FIGURE 7 is a diagram showing the dispersion curve
a manner as to permit the free expansion thereof as pro- .
of a delay line circuit in accordance with the present in
vided, for example, in the French Patent 1,086,890 of
vent-ion constructed according to FIGURE 4;
July 18, 1953, ‘also taken out in the name of the assignee
FIGURE ‘8 is a partial perspective view of a modi?ed
30
of the present application.
embodiment of a delay line circuit in accordance with
The prior art structure described hereinabove which
the present invention showing a further development of
utilizes the arrangements mentioned hereinabove entails
the delay line illustrated in FIGURE 4;
‘
the defect which consists in the possible propagation, in
FIGURE 9 is a transverse cross-sectional view of still
addition of the desired symmetric mode, of an anti-sym
metric or asymmetric mode for the propagation of which 35 another modi?ed embodiment of a delay line circuit in
accordance with the present invention;
the dimension of the gap, slot or separation in the bars
or delay line elements plays an essential role. Theoretical
calculations and actual measurements in ‘tests indicate that
the dispersion curve of this latter mode diifers only little
in the usual cases from the principal propagation, the
curve being simply displaced slightly toward the lower
FIGURE 10 is a plan view of the delay line circuit of
FIGURE 9 in accordance with the present invention, and
FIGURE 11 is a transverse cross~sectional view taken
along line 1I-11 of FIGURE 10.
'
ing to both the propagation of the symmetric mode ‘and
The present invention essentially consists in a delay
line circuit which is mechanically sturdy and free to ex
pand for use with travelling wave tubes, and is constituted
anti-symmetric mode on wave lengths which are not very
of a series of identical conducting elements ‘that are T-'
frequencies. With a given phase velocity thus correspond
different from one another, the ampli?er may amplify 45 shaped, disposed in essentially parallel planes equidistant
from one another and aligned perpendicularly to these
simultaneously both modes which results in troubled func
planes, the delay line in accordance with the present in
tioning and in an undesirable operation of the tube.
vention being operatively disposed with respect 'to a con
The object of the present invention is a circuit for
ductive back plate disposed in proximity to the arm por
travelling wave tubes of relatively high power which is
electrically equivalent of the prior art structure de?ned 50 tions of the T-shaped elements, parallel to these arm‘
portions and on the side of the leg portions of the T’s of
hereinabove, which, as this prior art line, ‘also enjoys the
which the leg portions are electrically interconnected with
properties of mechanical sturdi-ness, and which also
each other.
permits the free expansion of the bars or elements of the
More particularly, the structure in accordance with the
delay line, but in which the wave length of the sym
metric mode and that of the anti-symmetric mode, with 55 present invention comprises a rectangular wave guide pro
vided with a longitudinal slot or gap in the plane of sym
a given phase velocity, are separated from each other by
metry of one of the walls thereof, and a series of T-shaped
an interval which‘ is much greater than in the preceding
delay line elements of which the leg portions pass through.
case of ‘the prior art structure by such an extent that am
the gap or slot essentially perpendicularly to the slotted
pli?cation of the antisymmetric mode will not take place
since the interaction thereof with the beam, if it takes 60 wall portion and secured to the bottom of the guide at
a constant distance between the respective points where
place on the wave length of the symmetric mode, will not
they are secured thereto whereas the arm portions ofthe
occur on that of the anti-symmetric rnode.
T’s extend perpendicularly to the gap or slot and in paral
Accordingly, it is an object of the present invention to
lel to the external face of the wall portion which forms
provide a delay line structure for high-power travelling
wave tubes which obviates the disadvantages of the prior 65 the back plate, these arm portions thereby forming bars,
art.
of which the ends thereof are free.
.
Referring now to the drawing wherein like reference
numeralsware used throughout the various views to desig
nate like parts, ‘and more particularly to‘ FIGURE 1
which is mechanically sturdy and adapted to readily dissipate large quantities of heat.
.
70 thereof, the delay line circuit illustrated therein utilizes.
an arrangement represented by a combination of the teach
Still another object of the present invention is the pro
ings of the aforementioned French Patents 1,068,673
vision of a delay line structure for high—power travelling
- Another object of the present invention is the provision
of a delay line circuit for high-power travelling wave tubes
3,086,180
‘
4
3
and 1,086,890. The bars or individual elements 1 of ‘the
ladder, cut in the center thereof by means of slots 2, are
supported by lateral cheek portions 3 forming the sup
ports of the ladder and secured to a common base 4.
On this same common base 4 is disposed a :so-called “back
lency no longer exists between FIGURES 1 and 4 with
respect to the approximate equality of the wave lengths
for the symmetric and anti-symmetric modes. Indeed,
the circuit of FIG. 4 is utilisable in the symmetric mode
over a band centered on the wave length which is equal
plate” 5 of which the ‘surface is parallel to the bars 1
and relatively close thereto.
The structure illustrated in FIGURE 1 is mechanically
robust and sturdy, assures a isu?iciently Weak dispersion
to four times the sum of the lengths of the leg portion
pansion of the bars or delay elements 1. However, the
delay line circuit of FIGURE 1 exhibits a serious disad
vantage which will be better understood by reference to
FIGURES 2 and 3 which represent schematically bar
then indicates the ?eld distribution corresponding to this
mode and shows that the ?eld, which has a node at the
bottom of the leg portion of the T, increases in a sinu
and one arm portion of a T (AB and BC or BD in FIGS.
5 and 6). This means, for ABzBC, that the width CD
of the line is a quarter of the wave length of propaga
of ‘the fundamental forward wave and permits a free ex 10 tion of the symmetric mode. The curve 12 of FIG. 5
soidal Way along the leg portion till the middle B of the
type ladder structures which are ‘integral or uncut and cut, 15 bar, and then from point B the amplitude attained there
respectively.
at increases symmetrically toward the bar extremities C
and D where the anti-nodes of the ?eld take place.
‘FIG. 6 shows in 13 the ?eld distributions of the anti
the propagation in the useful band of frequencies takes
symmetric mode. It is seen that the anti-nodes or loops
place at a single symmetric mode producing on the bars 20 take place at C and D, but a node is produced in the mid
thereof a ?eld distribution having the ‘general shape or
dle point B. Since the ?eld is also nil in A, there is no
Whereas in the case of a bar-type ladder structure
which is uncut or integral as illustrated in FIGURE 2,
outline of a half-sinusoid with the nodes thereof at the
place of support, as illustrated by curve 6, the bar-type
ladder structure which is cut, as shown in FIGURE 3, per
?eld along the leg portion AB. Thus, the width CD of
the line is equal to half the wave length of propagation
of the anti-symmetric mode.
mits, in addition to this symmetric mode of propagation, 25
It is seen that there is a considerable difference be
the propagation of the anti-symmetric mode of which the
tween the wave lengths of the two modes since the same
?eld distribution, as illustrated ‘by curve 7 in FIGURE
3, is composed essenitally of two quarts of a sinusoid
width CD of the line corresponds to a quarter of a
length in one case and to half a wave length in the
also with the nodes thereof at the supports but with an
other case.
abrupt phase variation at the capacity formed in the mid 30
This result has been con?rmed experimentally by plot
dle of each bar by the free ends of the two half-bars
ting the dispersion curves for a certain circuit constructed
whereby the anti-nodes of the voltage at the ends of the
according to FIGURE 4, intended for use in a tube pro
two half-bars have opposite polarities.
vided for a hand between 23 and 40 cm. These curves are
It should be noted that whereas for the symmetric
shown in FIGURE 7 in the form of diagrams plotting the
mode the half wave length corresponds to the dimension 35 delay ratio c/vph, where c=speed of light, and vph=phase
of the line, for the antisymmetric mode of the cut bar,
velocity of the wave, as a function of the wave length A.
the half wave length is also very close to the dimension
Within the angle comprised between the axis of abscissa
of the line, the deviation from‘ an exact coincidence
and the straight of c/vph'=)\/2p, where p is the pitch of
therebetween being only due to the proximitiy of facing
the structure, this straight line representing the location
bars. Consequently, the symmetric mode and anti-sym 40 of the 11' modes, there is found a curve 14 representing
metric mode propagate on very closely adjacent wave
lengths, so much so that the latter may impair the ampli
the dispersion of the fundamental space wave of the sym
metric mode and a curve 15 representing the dispersion
?cation of the former in an undesirable manner. Fur
of the fundamental space wave of the anti-symmetric
thermore, this anti-symmetric mode is likely to be com
mode. It may be readily seen that for a given value of
pletely re?ected at the input and output of the tube so 45 c/vph, the wave lengths of the two modes are about at
that auto-oscillations may well be set up therein.
the ratio of 1:2 which locates the anti-symmetric mode
The circuit illustrated in perspective in FIGURE 4
outside the zone of interaction corresponding to the am
eliminates these inconveniences and disadvantages, while
pli?cation of the symmetric mode.
at the same time, retaining all of the advantages obtain
FIGURE 8 in which the same reference numerals are
50
able with the structure of FIGURE 1. The delay line
used to designate the same elements as in FIGURE 4,
circuit of FIGURE 4 comprises a rectangular guide 8
represents a further development in accordance with the
provided with a longitudinal gap or slot 9 in the plane
present invention which essentially consists of placing,
of symmetry of the wall 10 thereof and with a series of
side by side, several of the delay circuits of FIGURE 4,
T-shaped delay elements 11 of which the leg portions
pass through the slot 9 essentially perpendicularly to the
wall 10 and are secured or ?xed to the bottom of the
guide 8, the distance between adjacent points where the
leg portions are secured to the bottom 8 of the guide
being constant or essentially equidistant from one an
other which imparts a characteristic of geometric peri
odicity to the structure.
The arm portions of the T
shaped elements 11 extend essentially perpendicularly to
the gap 9 and essentially in parallel to the external face of
the wall portion 10 which forms the “back-plate.” These
for example, two circuits thereof including, respectively,
the series of T-shaped delay line elements designated by
reference numerals 11 and 11'. The circuit resulting
from such an arrangement is thereby periodic not only in
the direction perpendicular to the bars, but also in the
direction of the alignment of the homologous bars of
60 juxtaposed delay circuits. Such a circuit is particularly
suitable for use with tubes of very high power and also '
with all those tubes in which periodic bi-dimensional
structures can be used.
FIGURES 9, 10 and 11 represent a still further de
arm portions thus form the bars of which the ends are 65 velopment of a delay line structure of FIGURE 8 ac
free.
cording to the present invention which includes certain
The structure of FIG. 4 may be considered as a ?lter
as well as the known structure of FIG. 1. The two struc
improvements over the same.
cuit of FIG. 4 has the same sturdiness and the same free
through 11 essentially consists in effectively increasing
A ?rst improvement of the delay line structure of FIG
tures consequently may be employed for the same appli
URES 9 through 11 resides in the fact that it enables an
cations.
70 increased accentuation of the separation between the
It is seen that such an electrically equivalent structure
symmetric mode and the anti-symmetric mode of propa
also displays the same mechanical qualities, i.e. the cir
gation. This ?rst improvement according to FIGURES 9
dom of expansion of the bars as the circuit of FIG. 1.
the capacitive coupling between the free ends of the arm
However, as shown in FIGURES 5 and 6, the equiva 75 portions of'the T-shaped elements which face one another
3,086,180
5
r
6
t
of the ‘leg portions of said T-shaped members, said back
plate being provided with aperture ,means for receiving
by the fact of the juxtaposition alongside one another,
for example, by terminating the ends thereof in a step
like manner and by interdigitating the stepped ends.
A second improvement which may be obtained with
therein the leg portions, and means additional to and
spaced from said back plate and electrically connected
thereto for electrically interconnecting the extremities of
said leg portions remote from said arm portions.
2. A delay circuit as claimed in claim 1, wherein the
planes of said T-shaped members are equidistant, thereby
forming a geometrically periodical structure in the direc
a structure in accordance with FIGURES 9 through 11
permits an enlargement of the useful band of the line
and consists in providing ridges along the external surface
of the guide.
.
.
As in FIGURE 8, the delay circuit according to FIG
URES 9 through 111 comprises a wave guide 8 composed, 10 ition of alignment thereof.
3. A delay circuit for microwaves, comprising a plu
for example, of two rectangular wave guides placed
rality of series of substantially identical T-shaped con
alongside each other, provided with two longitudinal
ductive delay members each having'symmetrically ar
slots 9 and 9' in the upper wall 10 thereof. The delay
ranged arm portions and a leg portion disposed essential
elements 11 and 11’ have the shape of T’s, of which the
ly in the center of said arm portions, said members being
leg portions ‘pass respectively through the slots 9 and 9’
respectively located in essentially parallel planes and
and are secured at the bottom thereof to the bottom of
the guide 8 whereas the arm portions 16 and 16’ of the
T’s extend essentially in parallel to the Wall 10 and per
pendicularly to the slots or gaps 9 and 9'. One end of
each of the arm portions-16 faces the end of. an adjacent 20
aligned in a direction at an angle to said planes, said
respective series being located side by side one directly
following another so that the arm portions of respective
T-shaped members are essentially aligned in the direc
homologous arms portion 16,’ Each respective series of
delay elements 11 and 11’ includes elements periodically
spaced in the longitudinal direction of the delay line.
tions of said arm portions, conductive back plate means
According to the ?rst improvement of this line men
thereof, and means including an electrically conductive
extending essentially in parallel to said arm portions and
in proximity thereto ‘along the side of the leg portions
tioned hereinabove, the capacitive coupling between ends 25 member in addition to said conductive back plate means
and electrically connected thereto for electrically inter—
facing one another of each pair of arm portions 16 and
connecting the extremities of said leg portions remote
16’ is increased, by terminating the ends thereof in the
form of stepped portions 17 and 17’ and by interdigitating
from said arm portions.
.
4. A delay circuit as claimed in claim 3, comprising
these step portions 17 and 17’ in such a manner that they
means for increasing the capacitive coupling between
are separated by a spacing, slot or gap .18 in the form of
neighboring extremities of said arm portions belonging‘
zigzag or Z.
‘
‘
respectively to adjacent series of delay members.
Actual measurements have indicated that the separa
5. A delay circuit as claimed in claim 4, wherein said
tion between the symmetric mode and the anti-symmetric
extremities are stepwise shaped, and adjacent step-shaped
mode is further enhanced by a structure according to
FIGURES 9-11 as compared to the structures of the em
35 extremities are interdigitated.
6. A delay circuit as claimed in claim 5, further com
prising means in said delay circuit for increasing the effec
face 10 of the delay line structure in such a manner as
tive band thereof.
7. A delay circuit as claimed in claim 6, wherein‘ said
to engage between successive T’s as shown in FIGURE
11 which produces the second improvement mentioned 40 last-mentioned means are formed by ridges extending be
tween said arm portions.
hereinabove, namely the. increase in band Width.
8.‘ A delay circuit as claimed in claim 3, further com
While we have shown and described several embodi
prising means in said delay circuit for increasing the effec
ments in accordancewith ,the present invention, it is
tive band thereof.
understood that the same isrnot limited thereto but is
susceptible of many changes and modi?cations within 45 9. A delay circuit as claimed in claim 8, wherein said
last-mentioned means are vformed by ridges extending be
the spirit and scope-of the present invention, as known
bodiment ‘of FIGURE 8. "
The ridges 19 may additionally be provided on the sur
to a person skilled in the art. In particular, the rectilinear
tween said arm portions.
-
guides illustrated in FIGURES 4, 8, or 9 through 11 may
be effectively wound or bent into cylindrical form, about
_10. A delay circuit adapted to propagate a predeter
tionally, or in the alternative, the number of juxtaposed
plurality of essentially similar delay elements arranged
mined desired mode for use in relatively high-power
an axis either parallel or perpendicular to the bars. Addi 50 travelling =wave ampli?er tubes or the like comprising a
circuits shown in FIGURES'S or 9 through 11 is suscep
toprovide a periodic structure, each delay element com
tible of change, any suitable number being usable, and
prising at least two portions disposed at an angle to each
the cross section of the T-shaped elements either across
other and extending in different directions, the two por
the leg portions thereof or across the bars thereof may 55 hum of each delay element being rigidly connected with
receive any other desired shape as dictated by the needs
each other, and means operatively connected with said
of the practical use, constructions and applications.
Thus, it is quite obvious that the present invention is
not limited to the particular delay line circuits illustrated
herein, but may be varied at will within the spirit and 60
scope of the present invention and ‘we, therefore, do not
wish to be limited to the particular embodiments described
and illustrated herein, but intend to cover all such changes
and modi?cations as are encompassed by the scope of
the appended claims.
We claim:
1. A delay circuit for microwaves, comprising at least
one series of substantially identical T-shaped conductive
delay members each including symmetric arm portions
and a leg portion having a length essentially of the order
of the length of an arm portion, said members being re-‘
delay circuit for preventing the propagation in said delay
circult of an anti-symmetric mode near the operating
‘frequencies of said desired symmetric mode including
conductive means formed by a hollow wave guide pro
,vided with aperture means for receiving therein a ?rst
portion of each delay element and operable-to thereby
electrically interconnect a ?rst portion of each delay ele
ment While each second portion thereof has at least one
65 free end extending at a distance from said conductive
means on the outside of and spaced from the Walls of said
Wave guide thereby providing a predetermined electric
?eld distribution between said second portions and the
walls of said wave guide.
11. A delay circuit adapted to propagate therethrough
spectively located in essentially parallel planes and aligned
a predetermined desired mode for use in relatively high
power travelling wave ampli?er tubes or the like, com
in a direction at an angle to said planes, a conductive
prising a plurality of essentially similar delay elements
back plate extending parallel to the arm portions of said
arranged to provide a periodic structure, each delay ele
T-shaped members and in proximity thereto on the side 75 ment comprising at least two connected portions disposed
7
at an angle to each other and extending in mutually differ
ent directions, and means operatively connected with
said delay circuit for preventing the propagation in. said
delay circuit of an anti-symmetric mode near the operat
ing frequencies of said desired symmetric mode including
?rst conductive means electrically interconnecting a ?rst
portion of each delay element and second conductive
means electrically connected to said ?rst conductive means
5%
slot and ?xed inside the wave guide to the other broad
Wall thereof, the length of said bars being substantially
equal to the width of said broad walls, while the length
\ of said supports is somewhat more than the width of said
narrow walls.
19. A delay line structure comprising a metallic wave
guide provided with a longitudinal slot, and a number
of identical delay members of essentially T-shape includ
ing two arm portions and a leg portion, said leg portion
and extending at a relatively small distance from and at
least over a major area of the second portion of each 10 extending through said slot and being electrically con
delay element to thereby provide a predetermined electric
nected with the inner face of the wave guide opposite said
?eld distribution along both portions of each delay ele
slot while the arm portions of said T-shaped delay mem
bers extend along the outside of said wave guide, the
1.2. A bi-dimensional structure delay circuit according
outer surface of said wave guide adjacent said arm por
to claim 11, composed of at least two of said delay cir 15 tions eliectively constituting a conductive back plate there
cuits placed alongside one another.
for.
13. A bi-dimensional delay circuit structure according
20. A delay circuit for microwaves, comprising at least
to claim 12, further comprising means in said structure
one series of substantially identical T-shaped conductive
increasing the effective capacitive coupling between rnu~
delay members each including symmetric arm portions and
tually facing second portions of respective delay circuits. 20 a leg portion having a length essentially of the order of
14. A bi-dimensional delay circuit structure according
the length of an arm portion, said members being respec
to claim 13, further comprising means in said structure
tively located in essentially parallel planes and aligned in
ment.
increasing the effective band thereof.
15. A delay line structure comprising a rectangular
metallic wave guide having two broad and two narrow
Walls, one of the broad walls being provided with a lon
gitudinal slot in the middle thereof, and a number of
identical equidistant metallic bars disposed outside said
wave guide in close, parallel and transverse relationship
to said slotted wall, each of said bars being supported
in the middle thereof by a metallic support traversing
said slot and ?xed inside the Wave guide to the other
broad wall thereof.
16. A delay structure as claimed in claim 15, wherein
each bar is integral with its support and forms a T
shaped element.
a direction at an angle to said planes, a conductive back
plate extending parallel to the arm portions of said T
shaped members and in proximity thereto on the side of
the leg portions of said T-shaped members, said back
plate being constituted by a wall of a wave guide pro
vided with at least one slot, said T leg portions passing
through said slot, and means for electrically interconnect
ing the extremities of said leg portions remote from the
arm portions by securing said leg portions to the bottom
wall of said wave guide opposite said slot.
21. A delay circuit as claimed in claim 20, wherein
the wall forming said back plate is provided with ridges
which are essentially parallel to said arm portions and
engage between successive members thereof.
17. A delay structure as claimed in claim 15, wherein
the bars are substantially twice as long as the supports.
18. A delay line structure comprising a rectangular
metallic wave guide having two broad and two narrow 40
walls, one of the broad walls being provided with a lon
gitudinal slot in the middle thereof, and a number of
identical equidistant metallic bars disposed outside said
wave guide in close, parallel and transverse relationship
to said slotted wall, each of said bars being supported in
the middle thereof by a metallic support traversing said
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,197,338
2,730,678
2,879,437
2,888,597
Fritz _______________ __ Apr.
Dohler et al. _________ __ Jan.
Leblond _____________ __ Mar.
Dohler et al. _________ __ May
16,
10,
24,
26,
1940
1956
1959
1959
FOREIGN PATENTS
946,688
France ______________ __ Dec. 27, 1948
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